JP2003024725A - Opened cell structure for air filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an opened cell structure for an air filter provided with improved capability of removing object substances to be adsorbed while suppressing increase of pressure loss. SOLUTION: The opened cell structure is composed of a large number of air flow paths which are surrounded with a filtration material sheet containing a gas adsorbent and a thermoplastic resin and accumulated in parallel and the opened cell structure has 20% or higher aperture ratio in the transverse cross-section rectangular to the air flow paths, 0.35 g/cm<3> or higher density of the filtration material sheet, and 1.0 m<2> /L or wider cell surface area per unit volume of the opened cell structure itself.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an open cell structure for an air filter, and more particularly to an open cell structure for an air filter that improves the ability of an air filter to remove a substance to be adsorbed.

[0002]

2. Description of the Related Art For air cleaner filters and clean room chemical filters that remove toxic gases in the air,
BACKGROUND ART A filter medium sheet prepared by mixing a gas adsorbent with a substrate such as pulp and making a paper into an open cell structure is widely used. The open cell structure refers to a structure in which a large number of cells are integrated in parallel, with a tubular airflow passage surrounded by a filter medium sheet as cells, and typically a honeycomb structure. By passing air from one end to the other end of this open cell structure, the harmful gas is removed by the gas adsorbent contained in the filter medium sheet.

In the air filter having the open cell structure, the surface area in contact with air is increased as the number of cells per unit cross-sectional area of the cross section orthogonal to the air passage direction is increased by miniaturizing the cells, which is harmful. The gas removal performance can be improved. However, when the cells are miniaturized to increase the number of cells per unit cross-sectional area, the ratio of the opening area per unit cross-sectional area in the cross section orthogonal to the air passage direction,
That is, since the aperture ratio is reduced, there is a problem that the pressure loss of the air filter is increased and the load on the blower for forcibly circulating the air is increased.

From the above background, it has been necessary for the conventional open cell structure to have an aperture ratio of at least 20% in order to maintain the pressure loss at an acceptable level.

As described above, the means for maintaining the aperture ratio at 20% or more and increasing the contact area with air is to reduce the basis weight of the filter medium sheet to make it thinner, but the gas that can be filled in the filter medium sheet. Since the amount of the adsorbent is reduced, there is a problem that the ability of the air filter to remove the substance to be adsorbed is reduced.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an open cell structure for an air filter, which has an improved ability to remove substances to be adsorbed while suppressing an increase in pressure loss.

[0007]

In the open cell structure for an air filter of the present invention which achieves the above object, a number of air passages surrounded by a filter medium sheet containing a gas adsorbent and a thermoplastic resin are arranged in parallel. An integrated open cell structure having an opening ratio of 20% or more in a cross section orthogonal to the air passage, a density of the filter medium sheet of 0.35 g / cm ³ or more, and a unit volume of the open cell structure. Cell surface area of 1.0m
It is characterized by being ² / L or more (L: liter).

As described above, since the density of the filter medium sheet constituting the open cell structure is set to 0.35 g / cm ³ or more, the aperture ratio of the open cell structure is maintained at 20% or more and the open cell structure is formed. It is possible to make the cell surface area per unit volume of 1.0 m ² / L or more, and it is possible to improve the adsorption target substance removal ability of the air filter without increasing the pressure loss of the air filter. .

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The open cell structure for an air filter of the present invention is processed into a honeycomb structure or the like by using a filter medium sheet obtained by forming a gas adsorbent, a thermoplastic resin or the like into a sheet by a wet papermaking method. This is a structure in which the airflow passages of are integrated in parallel.

The filter medium sheet constituting the open cell structure for an air filter of the present invention has a density of 0.35 g / cm ³ or more, preferably 0.4 g / cm ^{3 to} 1.0 g / c.
m is ^3. As described above, by increasing the density of the filter medium sheet, the filter medium sheet can be thinned without reducing the basis weight of the filter medium sheet. Therefore, when forming an open cell structure, the aperture ratio is set to 20% or more to maintain the pressure loss at an allowable level, and the size of each cell is miniaturized to obtain a cross section orthogonal to the air passage direction. Since the number of cells per unit cross-sectional area is increased and the cell surface area is increased, the ability of the air filter to remove the adsorption target substance can be improved. The adsorption target substance removal capability is how long the adsorption target substance can be maintained at a predetermined removal rate or more when the adsorption target substance is passed through the air filter, and the maintenance time is long. The better.

As a method for densifying the filter medium sheet,
Heat consolidation treatment is preferred. By carrying out the heat consolidation treatment, the filter medium sheet can be thinned without reducing the basis weight of the filter medium sheet.

As a method of the heat consolidation treatment, a heat calendar treatment is preferable. When the filter medium sheet is produced by wet papermaking, the heating and consolidation treatment is performed online after the papermaking drying step or offline as a post-processing by a heating calendar treatment. In the heating calendering process, two rolls are installed in parallel with each other with a predetermined gap between them.
One roll is heated by electricity or steam, and while it is being rotated, the filter material after papermaking is dried is inserted into the gap, and the filter material is heated and compressed by two rolls while adjusting the thickness by controlling the pressure of the hydraulic cylinder. Done by.

The roll used for the heating calender treatment is usually a plain roll whose surface is treated flat, but in order to further improve the adsorption performance of the gas to be treated, an embossing roll is used, and a filter medium sheet is used. It is preferable to form fine irregularities on the surface. The uneven pattern includes dots, lines, etc., but when the surface area of the sheet is increased and the gas passes through the cells of the open cell structure,
Any material may be used as long as it causes turbulence of the air flow on the cell surface.

The filter medium sheet constituting the open cell structure of the present invention preferably contains at least a gas adsorbent and a thermoplastic resin and has a basis weight of 50 to 300 g / m ² . More preferably, the basis weight is 100 to 250 g / m ^2.
Is. If it is less than 50 g / m ² , sufficient gas adsorption cannot be obtained. Further, if it exceeds 300 g / m ² , the filter medium sheet becomes hard and the workability deteriorates.

As the gas adsorbent contained in the filter medium sheet, at least one selected from the group consisting of activated carbon, activated carbon fiber, ion exchange resin and ion exchange fiber can be selected, whereby a basic gas in the air can be selected. , Acid gas,
Any or all of the organic gas can be removed well.

The content of the gas adsorbent contained in the filter medium sheet is preferably 30 to 80 wt%. When the content of the gas adsorbent is less than 30 wt%, the gas adsorbing ability of the filter medium sheet decreases, and when it exceeds 80 wt%, the gas adsorbent falls off and the strength of the filter medium sheet decreases, which is not preferable.

The thermoplastic resin contained in the filter medium sheet functions not only as an aggregate but also as an adhesive agent when the filter medium sheet is processed into an open cell structure. Due to the inclusion of this thermoplastic resin, it is possible to perform the bonding only by heating the bonding portion. If an independent adhesive is used, the adhesive will cover the surface of the filter medium excessively, reducing the effective gas adsorption area.However, by using the thermoplastic resin as an adhesive that also serves as an aggregate, the minimum adhesion is achieved. The area enables the filter sheet to be bonded. As a result, even if the cells are miniaturized and the number of cells per unit cross-sectional area is increased, it is possible to minimize the increase in the area occupied by the adhesive part and suppress the deterioration of the adsorption performance of the air filter. Is possible.

Further, since the filter medium sheet contains a thermoplastic resin, in the wet papermaking of the filter medium sheet, the thermoplastic resin is melted in a heating process such as a drying process and the components contained in the filter medium sheet are adhered to each other. Therefore, the strength and rigidity of the filter medium sheet are improved.

The content of the thermoplastic resin in the filter medium sheet is preferably 5 to 30 wt%. More preferably 10
It is 20 wt%. When the content of the thermoplastic resin is less than 5 wt%, the heat fusion force of the thermoplastic resin is reduced, and 3
If it exceeds 0 wt%, diffusion of gas into the sheet tends to be insufficient, which is not preferable.

The thermoplastic resin used in the present invention is preferably a mixture or complex of at least two kinds of components having different melting points. With this, by adjusting the temperature so that only the low melting point component melts during the heat treatment,
The structure of the high-melting point component is retained, and appropriate voids can be generated inside the filter medium sheet.

Further, the thermoplastic resin is preferably a heat-sealable conjugate fiber having a core-sheath structure in which the melting point of the core component is higher than that of the sheath component.

That is, by setting the temperature at which only the sheath component having a low melting point is melted, the form of the core component is maintained, so that the fibrous structure having a constant shape remains and the strength, rigidity and air permeability are improved. A more excellent filter medium sheet can be formed.

Further, when the filter medium sheet containing the heat-fusible composite fiber having the core-sheath structure is heat-consolidated by heating calendering or the like, if the calender roll temperature is adjusted to a temperature at which only the sheath component is melted, gas will be discharged into the sheet. It is possible to make the filter medium sheet thin in the state where the voids for diffusing inside are secured.

The melting point of the sheath component of the heat-fusible composite fiber having a core-sheath structure is preferably 80 to 200 ° C., and 100 to 1
50 ° C. is more preferable. If the melting point of the sheath component is less than 80 ° C., the drying temperature cannot be increased in the drying step in wet papermaking, and therefore it is necessary to carry out a drying operation for a long time at a low temperature, resulting in a marked decrease in production efficiency. When cellulose pulp or the like is contained in the filter medium sheet at a temperature of ℃ or more, it causes thermal decomposition and the like, physical properties such as strength of the filter medium sheet are deteriorated, and an organic gas called paper burning odor is generated. Occurs, and it is necessary to raise the temperature of the filter medium sheet in order to melt the sheath component of the core-sheath structure, which is not preferable because the energy cost deteriorates.

The thermoplastic resin can be selected from polyethylene, polypropylene, nylon, polyester, polyvinyl alcohol and the like, and copolymers containing these polymers as main components.

Further, pulp and other known additives may be added to the filter medium sheet.

The filter media sheet described above is processed into an open cell structure. The open cell structure used in the present invention is preferably a honeycomb structure, and among them, a corrugated honeycomb structure is particularly preferable.

The honeycomb structure referred to here is a structure in which cells composed of a large number of airflow passages are accumulated in parallel, and the cross-sectional shape of the cells in the cross section orthogonal to the gas passage direction is hexagonal or triangular. Alternatively, the cross-sectional shape is not particularly limited as long as it has another shape.

A corrugated honeycomb structure, which is one of the honeycomb structures, is formed by alternately stacking flat filter media sheets and corrugated corrugated filter media sheets by so-called corrugated board, and bonding their contact points to each other. The one-sided corrugated board material is laminated in a plurality of stages and processed into an integrated structure having a large number of parallel flow paths.

The cell surface area per unit volume of the open cell structure of the present invention is 1.0 m ² / L or more, preferably 1.2m ² /L~4.0m ² / L. 1.0 m ² /
If it is smaller than L, the contact area between the filter medium sheet and the gas is too small, so that the ability to remove the substance to be adsorbed becomes low. The surface area per unit volume of the open cell structure is the total surface area of the filter medium sheet constituting the cell in contact with the passing gas in 1 liter of the open cell structure.

The open area ratio of the open cell structure of the present invention is 20%.
It is above, and preferably 30% to 80%.

The open area ratio of the open cell structure refers to the ratio of the cross-sectional area of the space through which the gas flows to the total cross-sectional area of the open cell structure in the cross section orthogonal to the air passage direction of the open cell structure. That is, the aperture ratio (%) = (the cross-sectional area of the space portion in the cross section of the open cell structure / the total cross section of the cross section of the open cell structure) × 100.

This aperture ratio is obtained by binarizing (converting into black and white) an enlarged photograph of a cross section by image processing to obtain the total cross sectional area of the open cell structure and the cross sectional area of the space, and calculating the ratio by the above formula. It is obtained by doing.

The number of cells per unit cross-sectional area of the cross section of the open cell structure of the present invention orthogonal to the air passage direction is preferably 80 cells / 10 cm ² or more, and more preferably 150.
Cell / 10 cm ² or more. By setting it to 80 cells / 10 cm ² or more, the surface area per unit volume of the open cell structure can be increased, and the ability of the air filter to remove the adsorption target substance can be improved.

The content of the gas adsorbent in the unit volume of the open cell structure of the present invention is preferably 70 g / L or more. When the amount is 70 g / L or more, it is possible to improve the ability of the air filter to remove the substance to be adsorbed.

The weight of the filter medium sheet per volume of 1 liter of the open cell structure of the present invention, that is, the packing density of the filter medium is preferably 100 g / L or more, more preferably 150 g / L or more.

FIG. 1 illustrates an open cell structure for an air filter of the present invention. The open cell structure is configured as a corrugated honeycomb structure 1, and as described above,
By so-called corrugated board processing, flat filter medium sheets 2 and corrugated corrugated filter medium sheets 3 are alternately stacked and bonded to each other at their contact points. This one-sided corrugated board material is laminated in a plurality of stages and processed into an integrated structure having a large number of parallel flow paths. In such a structure, the above-mentioned requirements are provided.

The open cell structure of the present invention can be used for various manufacturing devices in an air purifier, an air purifying system, a clean room, a semiconductor clean room used in a healthy house, a pet-friendly condominium, a facility for the elderly, a hospital, an office, or the like. It can be mounted on the wafer transfer path and used as an air filter for removing gaseous pollutants. Since the open cell structure of the present invention has a low pressure loss, it can be used in a low air volume circulation type air cleaning system. Also,
When used as a filter for removing gaseous pollutants in semiconductor-related clean rooms, semiconductor-related manufacturing equipment, or wafer transfer routes, there is very little dust generation due to powder falling, etc.
The load on the HEPA and ULPA filters arranged on the downstream side is small. Further, since no resin binder for papermaking or an adhesive for corrugating is used, outgas is not generated from the filter itself, and there is no chemical contamination behind the filter, which is preferable.

The air filter of the present invention is an air filter formed by using the above-mentioned open cell structure of the present invention, and is used as the above-mentioned air filter for removing gaseous pollutants.

[0040]

EXAMPLES Example 1, Comparative Examples 1 and 2, Conventional Example The material composition, the characteristics of the filter sheet and the characteristics of the corrugated structure were varied as shown in Table 1, and a filter sheet was prepared by wet papermaking. It was processed into an open cell structure (corrugated honeycomb structure) (Example 1, Comparative Examples 1 and 2, Conventional Example).

Each of the four types of open cell structures was used as an air filter, and air containing 10 ppb of ammonia gas was passed through at a surface wind velocity of 0.5 m / sec to conduct an ammonia gas removal test. The pressure loss of the air filter, the adsorption performance (ammonia removal rate of 90% or more) and the amount of outgas generated were measured by the methods shown. The results are shown in Table 1. The conditions other than those shown in Table 1 were the same.

Pressure loss: An evaluation filter is attached to the duct, and air is ventilated by a propeller fan or the like. At this time, the air flow rate is adjusted so as to match the target wind speed, and the pressure difference between the upstream side and the downstream side is measured. The wind speed is measured using a hot wire or ultrasonic anemometer, and the pressure difference is measured with a differential pressure gauge.

Adsorption performance (ammonia gas removal performance): An evaluation filter was attached to the duct, and the temperature was 23 ° C. and the humidity was 4
Air adjusted to 5% and an ammonia concentration of 5000 ppb was continuously aerated at a surface wind velocity of 0.5 m / sec, and the time required for the ammonia removal rate of the filter to decrease to 90% was measured. The results are shown by an index with the conventional example being 100, and the larger the value, the better the adsorption performance.

Amount of outgas generated: Temperature 23 at which the evaluation filter was attached to the duct and the activated carbon filter was ventilated.
Surface air velocity of 0.5m / s with clean air at ℃ and humidity of 45%
The concentration of all organic components in the upstream and downstream air was measured, and (downstream organic component concentration)-(upstream organic component concentration) was taken as the outgas generation amount. The collection of organic substances was carried out by passing the air branched from the duct through the solid adsorption tube for a certain period of time. The quantitative determination of the organic matter was carried out by introducing the heat-desorbed organic matter into the gas chromatography through the collected adsorption tube, and the case where the generation amount of the outgas which is 10 times or more of the generation amount of the example was observed was marked with x.

Comprehensive Evaluation: The judgment of the comprehensive evaluation was evaluated as × when any one of the judgment criteria of the following items was ×. Pressure loss: A pressure loss of 30% or more higher than that of the example was marked with x. Adsorption performance: Poor performance of 30% or more compared with the examples was marked with x. Outgas: Outgas that was generated 10 times or more as compared with the example was marked with x.

[0046]

[Table 1]

From Table 1, Example 1 in which heat-sealing fibers were used, calendering was performed to increase the sheet density, and the number of cells per unit cross-sectional area was increased to increase the surface area per unit volume was obtained. While suppressing the increase of pressure loss,
It can be seen that the adsorption performance (removal ability of the substance to be adsorbed) is improved and the amount of outgas generated is small.

[0048]

As described above, according to the present invention, the opening
The density of the filter medium sheet constituting the cell structure is 0.35 g / c
m³Because of the above, the open area ratio of the open cell structure is 20%.
% Or more and the unit volume of the open cell structure
Cell surface area of 1.0m ²/ L or more
Possible to increase the pressure loss of the air filter
To improve the ability of the air filter to remove the substances to be adsorbed.
It is possible to

[Brief description of drawings]

FIG. 1 is a perspective view showing a corrugated honeycomb structure which is one form of the open cell structure of the present invention.

[Explanation of symbols]

1 Corrugated honeycomb structure 2 Flat filter media sheet 3 Corrugated plate-shaped filter media sheet

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) B01J 20/20 B01J 20/20 BF 20/26 20/26 A 20/28 20/28 A D21H 15 / 00 D21H 15/00 27/10 27/10 F Term (Reference) 4D019 AA01 BA12 BA13 BB05 BC05 CA01 CB04 4D058 JA32 JB13 JB14 JB41 SA04 SA20 TA02 TA03 4G066 AA04B AA05B AC02C AC11B AC11C AE10B CA01 CA07 CA08 AF03 AF14 AF03 AF08 AF03 AF14 AF14 AF AF50 AG02 AG57 AG99 AH37 AH50 EA08 EA20 EA32 FA30 GA31

Claims (15)

[Claims] 1. An open cell structure in which a large number of air passages surrounded by a filter medium sheet containing a gas adsorbent and a thermoplastic resin are integrated in parallel, and an opening in a transverse section orthogonal to the air passages. An open cell structure for an air filter having a rate of 20% or more, a density of the filter medium sheet of 0.35 g / cm ³ or more, and a cell surface area per unit volume of the open cell structure of 1.0 m ² / L or more. 2. The open cell structure for an air filter according to claim 1, wherein the filter medium sheet contains pulp as a constituent material. 3. The open cell structure for an air filter according to claim 1, wherein the open cell structure is a honeycomb structure. 4. The open cell structure for an air filter according to claim 3, wherein the honeycomb structure is a corrugated honeycomb structure. 5. The air according to claim 1, wherein the number of cells per unit cross-sectional area of the cross section of the open cell structure orthogonal to the air passage is 80 cells / 10 cm ² or more. Open cell structure for filters. 6. The open cell structure for an air filter according to claim 1, wherein the content of the gas adsorbent in the open cell structure is 70 g / L or more. 7. The basis weight of the filter medium sheet is 50 to 300 g.
/ M ^{2 The} open cell structure for an air filter according to any one of claims 1 to 6. 8. The open cell structure for an air filter according to claim 1, wherein the filter medium sheet is heat-consolidated. 9. The air filter according to claim 1, wherein the content of the gas adsorbent in the filter medium sheet is 30 to 80 wt%, and the content of the thermoplastic resin is 5 to 30 wt%. Open cell structure. 10. The open cell structure for an air filter according to claim 1, wherein the surface of the filter medium sheet is subjected to a large number of irregularities. 11. The open cell structure for an air filter according to claim 1, wherein the gas adsorbent is at least one selected from activated carbon, activated carbon fiber, ion exchange resin and ion exchange fiber. body. 12. The open cell structure for an air filter according to claim 1, wherein the thermoplastic resin is a mixture or composite of at least two kinds of components having different melting points. 13. The thermoplastic resin is a composite fiber having a core-sheath structure, the core component has a higher melting point than the sheath component, and the sheath component has a melting point of 80 to 200 ° C. An open cell structure for an air filter according to claim 1. 14. The open cell structure for an air filter according to claim 1, which is mounted as an air filter on various manufacturing apparatuses in an air cleaner, a clean room, a semiconductor clean room or a wafer transfer path. 15. An air filter having the open cell structure for an air filter according to claim 1.